1. Field of the Invention
The present invention relates generally to an improved data processing system, and in particular, to a method and apparatus for providing backward compatibility on magnetic tape. Still more particularly, the present invention provides a method and apparatus for creating a format identification burst that is readable by tape systems employing different formats.
2. Background of the Invention
Magnetic tape is a sequential storage medium used for data collection, backup, and historical purposes. Magnetic tape is made of flexible plastic with one side coated with a ferromagnetic material. Magnetic tapes come in reels and cartridges of many sizes and shapes. In older systems, open reels are used while most presently available systems employ cartridges to hold the magnetic tape.
Data is written serially onto magnetic tape and must be accessed in a serial fashion. Locating a specific record on tape requires reading every record in front of it or searching for markers that identify predefined partitions. Although most tapes are used for archiving rather than routine updating, some drives allow rewriting in place if the byte count does not change. Otherwise, updating requires copying files from the original tape to a blank tape (scratch tape) and adding the new data in between.
Tracks either run parallel to the edge of the tape (linear recording) or diagonally (helical scan). For information storage and retrieval, magnetic tape has proven especially reliable, cost efficient and easy to use. In an effort to make magnetic tape even more useful and cost effective, attempts have been made to store more information per given width and length of tape. This increase in storage has generally been accomplished by including more data tracks on a given width of tape. While allowing more data to be stored, this increase in the number of data tracks results in those tracks being more densely packed onto the tape.
With increasing the number of tracks, the width of each track on a magnetic tape has decreased. With higher density in the number of tracks, different tape formats for recording data are present for the different track widths. Newer tape systems are often designed to be backward compatible, allowing them to read tapes written by older systems, having wider track widths. Older tape systems, however, are unable to read data written by newer systems. This situation sometimes may result in a magnetic tape having data written on a newer tape system being inadvertently overwritten with data by an older tape system because the older tape system is unable to detect the presence of data on the magnetic tape.
Therefore, it would be advantageous to have an improved method, apparatus, and computer instructions for detecting a tape format written to tape by both newer and older tape systems.